Scott was found dead Monday in her Manhattan apartment of an apparent suicide. In his Facebook post, Jagger said he's struggling to understand why she might have taken her own life. He called Scott his "lover and best friend."
"We spent many wonderful years together and had made a great life for ourselves. She had great presence and her talent was much admired, not least by me," he wrote. "I have been touched by the tributes that people have paid to her, and also the personal messages of support that I have received. I will never forget her."
Scott, 47, had been romantically linked to the Rolling Stones frontman for more than a decade. The Rolling Stones have called off tour dates in Australia and New Zealand following Scott's death. In a statement, the band said it is deeply sorry to announce the postponement of the rest of the tour. The Stones were scheduled to play this week and next week in several cities, including Perth, Melbourne and Sydney.
Meanwhile, details emerged in Britain about financial troubles that Scott's eponymous label had been experiencing. Last month the designer canceled her London Fashion Week show, due to reported production delays.
Scott was a renowned stylist and fashion designer whose clothes were worn by celebrities like Nicole Kidman, Angelina Jolie and Penelope Cruz.
The Associated Press contributed to this report.